A. Technical Field
The present invention relates to noise cancellation techniques, and more particularly to a method and system for actively canceling microphonics noise in radiation detectors using a multi-channel analyzer with an adaptive predictor for adaptive signal processing.
B. Description of the Related Art
High-purity Germanium (HPGe) detection systems are used to measure gamma ray spectroscopy to detect and identify radiological sources in the field. They do so by using highly sensitive preamplifiers which convert the electrons from each gamma ray detection event into an electrical signal. These detectors must operate at cryogenic temperatures and thus field operations require mechanical cooling solutions. Unfortunately, mechanical vibrations from the cooler are also converted to electrical signals by inducing changes in capacitance which are translated by the preamplifier into microphonic noise. To address the microphonics phenomenon, often a series of mechanical dampers and electrical filters are used to attenuate and cancel microphonic noise.
In the field of adaptive signal processing, adaptive filters (and adaptive processors generally) adapt their performance based on an input signal by self-adjusting their transfer functions according to an optimization algorithm. Such adaptive filters are often digital filters in a digital processing system for use in such example applications as speech-processing and noise cancellation, both of which involve continuous time processing where there are no periods in which the adaptation is switched between training and predicting.
In radiation detection applications and nuclear physics, however, adaptive filters and processers are not used in any of the four traditional configurations of prediction, system identification (modeling), equalization (deconvolving, inverse filtering, or inverse modeling) or interference canceling. There is a disconnect between the two fields of adaptive signal processing and nuclear physics because the signals in nuclear physics are random pulses for which only the timing, energy and occasionally the decay constant are considered useful. This is quite different from signal processing in which phase and magnitude of discrete versions of continuous time signals are considered.